1. Field of the Invention
This invention is directed to terminal modules for housing small circuits which are electrically connected across field wiring terminals and, more particularly, to moudlarized packages which are adapted for concurrent physical and electrical connection to two or more terminals on a frame containing a plurality of field wiring terminals. A primary application of the invention is in electrical data acquisition systems using microprocessors and other monitoring circuitry mounted on printed circuit boards to manage data input and output, such as for providing control and protection functions for systems in electrical power plants and generators.
2. Prior Art
Present day industrial electrical data acquisition and processing systems frequently require stacked termination frame assemblies or terminal connectors mounted typically in a cabinet with the field terminals accessible through a first door and with the circuit boards and component assemblies which are connected to other equipment in the cabinet being accessible through an opposite door. In such applications it is frequently required to have one or more electronic components mounted across the field wiring leads, i.e., not part of the circuit board assemblies and separately accessible. While such components could be made a part of the I/O electrical circuitry itself, frequently this is not possible or convenient. Thus, often it is desirable that the circuit boards to which the field terminals connect may be removed for maintenance without affecting the overall field system operation, which can be done if the components in question are separately connected to the field terminals. For example, one or more dropping resistors may be utilized in a field current loop, the dropping resistors being connected across the field terminals while the processing and analyzing circuitry receives its input from the dropping resistors.
A common prior practice in applications as referred to above is to physically terminate the wire leads of the electronic components directly to the screw terminals used for the field wiring. This arrangement not only gives the appearance of a last minute design change, but exposes the electronic component or components to physical damage during assembly, maintenance or other events. The performance and maintenance of the external components is sensitive to unforeseen installation mistakes, such as shorting of the component to the chassis where the proper assembly technique is not followed. Further, it is readily seen that where plural components are to be connected across two or more field terminals, the method of direct attachment of the components to the terminals becomes even less desirable.
A typical prior art approach has been to contain an external component in a potted box or other potting means, with metal connector blades or pins extending out of the potting material. Basically this constitutes simply an encapsulation of the component in order to protect it, and does not provide the desired ability to achieve reliable electrical and mechanical attachment.
There is thus a need in this art area for a standardized package and means of reliably connecting, both mechanically and electrically, external components to field screw terminals. This need has required an engineered packaging approach that permits housing of a plurality of small electronic components in a small, modular, lightweight and rugged assembly, and which provides reliable and quick attachment of the component module to the terminal assembly.